As a rubber composition used for a sidewall of a tire, a butadiene rubber (BR) has been blended for improving flex crack growth resistance in addition to a natural rubber (NR) exhibiting superior tear strength, and further, a carbon black has been used for improving weather resistance and reinforcing property.
However, environmental problems have been recently emphasized and regulations on CO2 emission have been made more rigorous. Further, since petroleum resources are finite and its supply quantity has been reduced year by year, petroleum price is predicted to surge in future and there is a limit in using raw materials derived from petroleum resources such as a BR and carbon black. Consequently, considering depletion of petroleum in future, it is necessary to use resources other than petroleum such as a NR and white fillers such as silica and calcium carbonate. However, if resources other than petroleum are used, properties such as flex crack growth resistance and reinforcing property are remarkably deteriorated compared with the case of using petroleum resources. Thus, even if resources other than petroleum are used, there are required equal or better properties such as flex crack growth resistance and reinforcing property compared with the case of petroleum resources having been used.
JP2003-63206A discloses raw materials for a tire assuming depletion of petroleum, but does not disclose a rubber composition for a sidewall that exhibits adequate flex resistance, reinforcing property and weather resistance.